This invention relates to a passenger restraint assembly having a sensor for detecting seat belt tension to indicate the presence of a child restraint seat.
Typically, a motor vehicle will include an air bag system to deploy an air bag cushion to protect passengers in the event of a collision. Air bag cushion deployment must necessarily be quick in order to prevent injury caused by the collision. The speed of deployment of the air bag cushion and the accompanying force of the inflating air bag cushion makes deployment of the air bag cushion to protect small children undesirable. Further, the use of a child restraint scat is not compatible with the intended operation of the air bag system- Although warnings of and prohibitions against the seating of children or the use of child restraint seats where an air bag may deploy are now standard in vehicles equipped with an air bag system, such warning may be ignored, causing undesirable results.
Passive warnings and notices may be supplemented with an active system that senses the type of occupant utilizing the seat and disables air bag deployment based on predetermined criteria. One such system known in the art is a weight based occupant detection system. A weight-based system includes sensors placed in the seat that allow a determination of the weight of the occupant in that seat. Such systems are set to disable the air bag upon a determination that an occupant is below a certain predetermined weight. Such systems work well, however, such a system can be fooled by the placement of child restraint seat over the weight sensors. Typically, the child restraint seat is secured to a seat of a motor vehicle by threading the seat belt around or through the child restraint seat. The seat belt of the motor vehicle does not actually secure the child as is normal when used to secure and adult. Instead the seat belt is used to secure the seat, and then the seat secures the child. Because the seat belt is securing the child restraint seat, it will be pulled tighter than when normally used to secure a human occupant. Pulling of the seat belt tightly around the child restraint seat will provide a large force on the seat, and thereby the weight sensors. Such a force can fool the weight sensor system into believing that a large adult is seated in the passenger seat rather than the child restraint seat and therefore not disable deployment of the air bag cushion.
For these reasons it is desirable and necessary to develop a method and device that can detect and differentiate between the presence of an adult occupant and a child restraint seat such that deployment of the air bag cushion can be disabled when the seat is occupied by a child restraint seat.
The invention is an assembly and method for sensing the tension forces on a seat belt such that a determination can be made as to the presence of a human occupant or a child restraint seat.
The assembly includes a seat belt attached to an interior support of the motor vehicle. Attached to the seat belt is a sensor that measures the tension forces exerted on the seat belt. Forces above a predetermined magnitude not tolerable by the human occupant indicates the presence of a child restraint seat and thereby provides the information needed to signal disable deployment of the air bag cushion. The sensor of a first embodiment is mounted in line with the seat belt by looping ends of the seat belt through the sensor. A center section of the sensor connects a strain gauge to detect tensile forces exerted on the seat belt. The strain gauge is electrically connected to a controller mounted within the motor vehicle for use in determining if deactivation of the air bag is necessary.
Another embodiment of the invention includes three prongs attached to a common beam. A middle prong includes the strain gauge that operates to sense movement relative to at least two outside prongs. The seat belt is threaded over the outside prongs and under the middle prong. This configuration provides for the installation of the sensor without modification to the seat belt. Tension on the seat belt operates to force the middle prong to move substantially perpendicular to the tension of the belt. The strain gauge mounted on the middle prong senses the amount of movement and signals the controller. The amount of movement of the middle prong is proportional to the tension force placed on the belt, which is used to determine the presence of an adult occupant or a child restraint seat.
The invention also includes a method of differentiating between the presence of a human occupant and a child restraint seat in a motor vehicle. The method includes the steps of sensing tension exerted on a seat belt, communicating the magnitude of the sensed tension to a controller, comparing the magnitude of tension to a predetermined tension, and determining that a child restraint seat is present if the sensed tension is greater than the predetermined tension.
The method and assembly of the subject invention provides the necessary information to detect and differentiate between the presence of an adult occupant and a child restraint seat such that deployment of a vehicle air bag can be prevented when a child restraint seat occupies the seat